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There are many kinds of materials for the production of bending machine tooling, including steel, cemented carbide, steel-bonded cemented carbide, zinc-based alloy, low melting point alloy, aluminum bronze, polymer materials and so on. At present, most of the materials used to manufacture stamping and bending machine tooling are steel. Commonly used materials for working parts of bending machine molds include: carbon tool steel, low alloy tool steel, high carbon high chromium or medium chromium tool steel, Medium-carbon alloy steel, high-speed steel, base steel, cemented carbide, steel-bonded cemented carbide, etc.
The following introduces several material knowledge:
1. Carbon Tool Steel
The most commonly used carbon tool steels in bending machine molds are T8A, T10A, etc., which have the advantages of good processing performance and low price. However, the harden ability and red hardness are poor, the heat treatment deformation is large, and the load-bearing capacity is low.
2. Low Alloy Tool Steel
Low-alloy tool steel is based on carbon tool steel with an appropriate amount of alloying elements. Compared with carbon tool steel, it reduces quenching deformation and cracking tendency, improves the harden ability of steel, and has better wear resistance. The low-alloy steels used in the manufacture of bending machine molds include CrWMn, 9Mn2V, 7CrSiMnMoV (code CH-1), 6CrNiSiMnMoV (code GD) and so on.
3. High Carbon and High Chromium Tool Steel
Commonly used high carbon and high chromium tool steels are Cr12, Cr12MoV, Cr12Mo1V1 (code D2), they have good harden ability, harden ability and wear resistance, heat treatment deformation is very small, for high wear resistance and micro deformation bending machine mold Steel, the carrying capacity is second only to high-speed steel. However,
the segregation of carbides is serious, and repeated upsetting (axial upsetting, radial upsetting) and forging must be carried out to reduce the unevenness of carbides and improve performance.
4. High Carbon Medium Chromium Tool Steel
The high-carbon medium-chromium tool steels used for bending machine molds include Cr4W2MoV, Cr6WV, Cr5MoV, etc. They have low chromium content, less eutectic carbides, uniform carbide distribution, small heat treatment deformation, and good harden ability. And dimensional stability. Compared with high carbon and high chromium steel with relatively serious carbide segregation, the performance is improved.
5. High-speed Steel
High-speed steel has the highest hardness, wear resistance and compressive strength among die steels for bending machines, and has a high load-bearing capacity. Commonly used in bending machine molds are W18Cr4V (code 8-4-1) and W6Mo5 Cr4V2 (code 6-5-4-2, US brand M2) with less tungsten content, as well as carbon and carbon reduction products developed to improve toughness. Vanadium high speed steel 6W6Mo5 Cr4V (code 6W6 or low carbon M2). High-speed steel also needs to be forged to improve its carbide distribution.
6. Base Steel
Add a small amount of other elements to the basic composition of high-speed steel, and appropriately increase or decrease the carbon content to improve the performance of the steel.
Such steel types are collectively referred to as base steel. They not only have the characteristics of high-speed steel, have a certain degree of wear resistance and hardness, but also have better fatigue strength and toughness than high-speed steel. They are high-strength and toughness cold-work bending machine die steels, and the material cost is lower than that of high-speed steel. The commonly used base steels in bending machine molds are 6Cr4W3Mo2VNb (code 65Nb), 7Cr7Mo2V2Si (code LD), 5Cr4Mo3SiMnVAL (code 012AL) and so on.
7. Cemented Carbide and Steel Bonded Cemented Carbide
The hardness and wear resistance of cemented carbide are higher than any other type of bending machine die steel, but the bending strength and toughness are poor. The cemented carbide used as the mold of the bending machine is tungsten-cobalt. For bending machine molds with low impact resistance and high wear resistance, cemented carbide with lower cobalt content can be selected. For high impact bending machine molds, cemented carbide with higher cobalt content can be selected.
Steel-bonded cemented carbide is made by adding a small amount of alloying element powder (such as chromium, molybdenum, tungsten, vanadium, etc.) to iron powder as a binder, using titanium carbide or tungsten carbide as the hard phase, and sintering by powder metallurgy. The matrix of steel-bonded cemented carbide is steel, which overcomes the disadvantages of poor toughness and difficult processing of cemented carbide. It can be cut, welded, forged and heat treated. Steel-bonded cemented carbide contains a lot of carbides. Although the hardness and wear resistance are lower than that of cemented carbide, it is still higher than other steel grades. After quenching and tempering, the hardness can reach 68 ~ 73HRC.
8. New Materials
The material used in the mold of the stamping CNC bending machine belongs to the mold steel of the cold work bending machine, which is the most widely used and widely used mold steel of the bending machine. The main performance requirements are strength, toughness, and wear resistance. At present, the development trend of cold work bending machine die steel is based on the performance of high alloy steel D2 (equivalent to my country’s Cr12MoV), divided into two major branches: one is to reduce the carbon content and the amount of alloying elements, and to increase the carbides in the steel The uniformity of the distribution highlights the improvement of the toughness of the bending machine mold. Such as 8CrMo2V2Si from Vanadium Alloy Steel Company in the United States and DC53 (Cr8Mo2SiV) from Datong Special Steel Company in Japan. The other is powder high-speed steel developed for the main purpose of improving wear resistance to adapt to high-speed, automated, and mass production. Such as 320CrVMo13 in Germany, etc.
The material of the bending machine tooling is the main key factor affecting the service life. If the material is selected well, the service life will be relatively prolonged without other variable factors.
Another Important Factor That Affects Service Life is The Heat Treatment Process During Processing.
1. whole body heat treatment and knife edge oxidation are completely two concepts. In order to save processing costs, some bending machine mold manufacturers do not undergo full-body heat treatment after the mold is formed, but oxidize the knife edges on the main parts of the bending machine. The hardness after oxidation is lower than the surface hardness after full-body heat treatment. Compared with the whole body heat treatment, the life of the mold with only simple knife edge oxidation is greatly reduced than that of the whole body heat treatment. This is one of them.
2. the choice of heat treatment process is also a key reason. Generally, the heat treatment process commonly used by mold manufacturers is high temperature furnace heat treatment. Although the surface of the mold can reach a certain hardness, the high temperature heat treatment process has drawbacks. The hardness of each part of the mold produced by high temperature heat treatment may be more or less certain. The difference is that what high temperature heat treatment can achieve is that the surface can reach the corresponding hardness. The deeper the inside, the lower the hardness will be. Therefore, the above two points will have an impact on the life of the mold.
Because of the different structure of different workpiece materials, the tools used are also different, and the resulting wear resistance, tensile strength, material hardness, tensile coefficient, plasticity, etc. are different. When choosing a mold, a reasonable choice can be made according to the pressure, structure, material, unfolded size of the workpiece, process requirements, surface treatment, etc. of the machine tool. Under normal circumstances, the width of the notch of the lower die can be selected for iron plates, which is 7-9 times of the material thickness, not less than 7 times. The notch of the stainless steel selection die is 6-8 times the material thickness, not less than 6 times. For aluminum and copper, the notch of the lower mold can be 6-8 times the thickness of the material, not less than 6 times (should avoid surface cracks during bending).
Customized tools are also available with following information:
- angles needs to be bended
2. The parts shape needs to have
3. Thickness/material of plate that for the part
4. Length of the part has to be bended
5. Requirement to the part (scratch possibility, Radius, parallelism, linearity)
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